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Andi - posted on 04/15/2011

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My son has mosaic Down syndrome. It's a more rare type of Ds (2-3% of Ds cases are mosaic). It differs in that with "regular" Ds, all of the cells are affected (i.e., have an extra chromosome). With mosaic Ds, that isn't the case - only a percentage of cells are affected (that percentage varies from person to person, and also within a person, so the percentage of affected blood cells may be different from the skin cells, etc.) Practically speaking, mosaic Ds tends, on average, to be a milder form, but that doesn't guarantee a better outcome for any one individual.